Python Driver pymongo, Integers inside array are converted to float

[Samuel Feng]

Dears,

Record in mongo shell(3.2.6):

> db.users.find({_id:ObjectId('576b8ba158e039761d94dcf6')}).pretty()

{

"_id" : ObjectId("576b8ba158e039761d94dcf6"),

"name" : "test",

"roles" : [1,9],

"point" : 0,

"createTime" : ISODate("2016-06-23T15:08:04.130Z")

} 

However, if retrieving this record using pymongo(3.2.2), the "roles" field above, which is array of int, are changed into array of float:

>>> from pymongo import MongoClient

>>> from bson.objectid import ObjectId

>>> client = MongoClient()

>>> db = client.ga

>>> doc = db.users.find_one({'_id':ObjectId('576b8ba158e039761d94dcf6')})

>>> print doc

{u'_id': ObjectId('576b8ba158e039761d94dcf6'), u'name': u'test', u'roles': [1.0, 9.0], u'point': 0, u'createTime': datetime.datetime(2016, 6, 23, 15, 8, 4, 130000)}

Is this behavior is expected? 

Thanks and Regards,

Samuel Feng

[Luke Lovett]

Hi Samuel,

The mongo shell uses as its language Javascript, which has only a "number" type, which is a floating-point number. This is the type of all numbers, unless they're wrapped in some other BSON type like Int64 (called "NumberLong" in the shell). The shell displays floats with no significant data after the decimal as just the portion before the decimal, so "1" is the same as "1.0". Python distinguishes between ints and floats, so the type of the numbers in "roles" becomes clear using Python.

This page provides some information about types in the mongo shell: https://docs.mongodb.com/manual/core/shell-types/.